Formula for tiered pricing

Hello,

I need to calculate spend based on the number of emails I send a month. The emails are priced using the below grid:

Up to 12k emails per month: Free
Next 1m emails per month (per thousand emails): $0.20
Next 5m emails per month (per thousand emails): $0.15
Remaining emails (per thousand): $0.10

So if I was sending 10,000,000 emails, it would work out like this:
TIER SENDS COST
Free 12,000 $0.00
$0.20 per thousand tier (next 1m) 1,000,000 - $200.00
$0.15 per thousand tier (next 5m) 5,000,000 - $750.00
$0.10 per thousand tier (remaining emails) 3,988,000 - $398.80
MONTHLY TOTAL 10,000,000 $1,348.8

Is there a single line formula I could use to calculate this? So number of emails, for example, is in A1, and I want the cost to show in A2.

Thanks!

Not a spammer - they're notification emails for an app, rather than emails from a person!

If it's at all helpful, we're using Mandrill: http://mandrill.com/pricing/

Someone on another forum managed to solve this for me, so I thought I'd post the answer here in case anyone else needs something similar.

=IF(AND(A1>12000,A1<=1000000),((A1-12000)/1000)*0.2,IF(AND(A1>1000000,A1<=5000000),200+((A1-1012000)/1000)*0.15,IF(A1>5000000,950+((A1-6012000)/1000)*0.1)))